Power transmission

ABSTRACT

Remote control of a directional control valve in a hydraulic power system is achieved through a pilot control circuit carrying a continuous flow of fluid through a fixed and a variable orifice in series. The variable pressure intermediate the orifices is applied in opposition to a spring system for achieving precise degree of opening of the directional valve and thus modulating the flow therethrough. The spring system achieves a fine and a coarse control of the output flow through the use of a high rate spring effective during initial opening travel of the valve. A flow rate limiter responsive to the pressure drop across an orifice in the main return flow line acts when this pressure drop becomes too high to override the remote control system and shift the main valve toward closed position. The control system is especially useful in hydraulic systems having a central power supply operating at a constant pressure to make fluid available selectively to any of a number of independent hydraulic motors, as for example for operating deck machinery on a ship.

United States Patent Primary Examiner-Henry T. Klinksiek Attorney-Van Meter and George ABSTRACT: Remote control of a directional control valve in a hydraulic power system is achieved through a pilot control circuit carrying a continuous flow of fluid through a fixed and a variable orifice in series. The variable pressure intermediate the orifices is applied in opposition to a spring system for achieving precise degree of opening of the directional valve and thus modulating the flow therethroughv The spring system achieves a fine and a coarse control of the output flow through the use of a high rate spring effective during initial opening travel of the valve. A flow rate limiter responsive to the pressure drop across an orifice in the main ,return flow line acts when this pressure drop becomes too high to override the remote control system and shift the main valve toward closed position. The control system is especially useful in hydraulic systems having a central power supply operating at a constant pressure to make fluid available selectively to any of a number of independent hydraulic motors, as for example for operating deck machinery on a ship.

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I N VEN TO R ROBERT H. BREEDEN ATTORNEYS POWER TRANSMISSION Hydraulic power transmission systems of the type having a central pressure supply operating at a nearly constant pressure for driving selectively any one or more of a plurality of hydraulic motors are widely used in many applications such as aircraft, farm tractors and the like, especially where a simple on-off control of the hydraulic motors is all that is necessary. Where a more precise modulation of the flow to the hydraulic motor is required, such systems have heretofore not been well suited except by using costly precision servocontrols. This is particularly true in systems where the operator's control handle must be at a distance from the directional valve which supplies fluid to a motor and where it is difficult or impossible to provide direct mechanical connection between the operator and the directional valve.

It is an object of the invention to provide a directional valv and a remote control system therefor which dispenses with mechanical connections between the remote controlling station and the valve, and which at the same time provides for precise modulation of the flow through the valve conveniently from the remote control station.

The sliding spool type of directional valve which is almost universally used in hydraulic systems does not lend itself readily to precise flow modulation because the rate of flow increase with each increment of spool travel is very high at small valve openings and falls off rapidly after the first few increments of spool travel. This characteristic increases the difficulty of achieving precise modulation when the spool travel is controlled from a distance.

It is an object also of the invention to provide a remote control system capable of application to a standard sliding spool directional valve with only minor modifications and which through the use of only pipe connections between the valve and the remote control station can provide a precise control of spool travel during its initial opening as well as throughout its full travel.

A further object is to provide in a valve of this type a simple flow limiting control which may be adjusted to hold the maximum flow through the valve at any desired level.

The invention consists in a valve for controlling fluid flow comprising a body having a laterally ported bore, a spool slidable in the bore to control flow between ports of the bore, pressure actuated pilot means for shifting the spool, a high-rate spring means positioned to oppose the pilot means during a portion of the spool travel, a low-rate spring means positioned to oppose the pilot means during at least the remainder of the spool travel, a yieldable abutment between the spool and the high-rate spring, fluid-operated means for controlling the yieldable abutment and means for applying and modulating a supply of pressure fluid to the pilot means.

FIG. 1 is a top view of a valve incorporating a preferred form of the present invention.

FIG. 2 is a side view of the valve of FIG. 1.

FIG. 3 is an end view of the valve of FIG. 1.

FIG. 4 is a circuit diagram of the valve and its controls.

FIG. 5 is a sectional view of a bypass valve incorporated in the controls.

FIG. 6 is a fragmentary view on a larger scale showing a portion of the valve of FIG. I, partly in section.

FIG. 7 is a top view of a remote control station forming part of the controls.

FIG. 8 is a side view of the control station of FIG. 7.

FIG. 9 is an end view of the control station of FIG. 7.

FIG. 10 is a fragmentary sectional view taken on line 10- 10 of FIG. 7.

The main directional control valve illustrated in FIGS. 1, 2 and 3 comprises a main body 10 having a pair of end caps 12 which are identical and which has an internal bore provided with the usual series of lateral ports for pressure for exhaust and for supply to either of the motor connections A and B. The central bore 14 in FIG. 6 carries a spool 16 for controlling the flow between the various lateral ports of the bore, as is well understood in the hydraulic art. External connection flanges are provided at 18 and 20, FIG. 3, for pressure and exhaust and a common flange at 22 is provided for connections to the motor passages A and B.

Valves of this type have not heretofore been well suited for use in central hydraulic systems wherein flow from a substantially constant pressure source must be modulated to control the operation of a fluid motor, since the degree of valve opening required for a given motor speed varies widely depending upon the load which the motor has to overcome. At very light loads, only a slight opening through the valve is required since a high degree of throttling at this point is necessary in order to control the operating speed of the motor. On the other hand, when the load is high, very little throttling is required and much wider openings of the valve are necessary to produce a given motor speed. These problems have been overcome to some extent by providing long tapers or tapered grooves on the spool heads, but this greatly increases the required size of the valve and introduces problems when the valve is to be pilot operated by fluid pressure.

Referring now to FIG. 4, the main directional control valve as a whole is there designated as 24, being illustrated in accordance with the international standard diagrammatic conventions, and as contained within the block designated I0I2. For the purpose of providing pilot pressure control, a circuit is established utilizing as a source of pressure the main pressure supply entering through the flange connection 18 and tapped off from the same by the line 26. This line may be contained in a block or sandwich plate 28 which can be bolted to the top of the body 10 as shown in FIG. 3. Line 26 leads to a second block or sandwich plate 30 within which the line 26 divides into branches 32 and 34 containing restrictions 36 and 38 respectively. The branch 36 has an arm 40 extending to one of the end caps 12 of the valve 24 and the branch 34 similarly has an arm 42 extending to the opposite end cap of the valve 24. Each of the arms 40 and 42 may have a variable restrictor with a check valve bypass as indicated at 44 for the purpose of regulating the rate of travel of the spool 16. The branches 32 and 34 also have arms 46 and 48 respectively which serve as the remote control connectors between the main directional valve and the remote control station indicated by the block 50. The anns 46 and 48 connect to a four-way directional valve 52 which is manually controlled at the remote location as will later be described. The directional valve 52 serves to reverse the connections of the two arms 46 and 48 to an adjustable pressure relief valve 54 and a direct exhaust line 56 respectively. That is to say, when one of the arms is connected to the relief valve 54, the other arm is connected directly to the exhaust line 56 and vice versa.

By means of a pilot control circuit of this kind, the spool of the main valve 24 may be given a modulating type of control from a remote location. There is a continual small flow from the high pressure supply line into the line 26 and out through the branches 32 and 34, through the restrictions 36 and 38, and through the arms 46 and 48 to the four-way directional valve 52, and ultimately from thence to the exhaust line 56. Depending upon the direction in which flow takes place through the valve 52, one or the other of the arms 46 and 48 will be exhausted directly to the line 56 and the other will be exhausted thereto through the adjustable pressure relief valve 54. Thus, by first shifting the four-way directional valve 52 and then by increasing the pressure on the spring of the relief valve 54, pressure may be built up in one or the other of the arms 46 and 48 and this pressure is reflected in one or the other of the arms 40 or 42 respectively. It is this control pressure which is applied within an end cap 12 and which opposes the spring means in the opposite end cap and thus enables an operator to exert a modulating type of control on the main valve 24.

In order to provide a convenient single lever control for the valves 52 and 54, the remote control station may be constructed as illustrated in FIGS. 7 through 10. Thus, the block 50 may be provided with internal passages such as 58 which connect with four-way valve 52 at the port 62 and with the external exhaust connection 64. Likewise, passage 66 connects with valve 52 at port 68 and with valve 54 at port 70. Ports 72 and 74 in the top of the four-way valve 52 are provided for connection with the remote control arms 46 and 48 respectively of the control circuit.

The valves 52 and 54 may be manually actuated from a single lever 76 through a suitable mechanical linkage such as provided by the double acting collapsible link 78 which has a pair of internal springs preloaded to yield only under a force significantly greater than that required to shift the four-way directional valve 52. When the later has reached its extreme position, one or the other of these springs will compress permitting further movement of the lever 76. The output end of the link 78 is connected to an arm 80 rigidly secured to a rotatable shaft 82 joumaled in bearings 84 on the base 50. A second arm 86 also rigidly secured to the shaft 82 is connected by a link 88 with the operating spool 90 of the valve 52. Thus, movement of the lever 76 through a small-angle to one side or the other of its central position will correspondingly shift the spool 90 of valve 52 to its left or right-hand limit of travel. Thereafter, further movement of the lever 76 compresses one or the other of the springs within the collapsible link 78.

Lever 76 is rigidly secured to a shaft 92 joumaled in a bearing block 94 and projecting from the opposite side thereof to engage within the central bore of an operating arm 96. The relation between the shaft 92 and the arm 96 is illustrated in FIG. 10. The arm 96 is pivoted to the base in a block 98 and has a link 100 pivoted at its upper end for exerting varying degrees of compression upon the spring of the adjustable relief valve 54. The shaft 92 has abutment surfaces 102 and 104 which contact abutments 106 and 108 respectively in the arm 96 after a predetermined degree of angular motion of the shaft 92. Thus, when the spool 90 of four-way valve 52 has been shifted to one extreme or the other, one pair of these abutments will come in contact and further angular motion of the shaft 92 will shift the link 100 to increase the compression of the spring in the relief valve 54.

Referring now to FIG. 6, there is illustrated the spring mechanism which offers differing force-displacement rates to oppose the manually varied pilot pressure at the opposite end of the main valve spool. FIG. 6 illustrates a construction which is duplicated at each end cap 12. With a spool 16 which has square-end heads along its length, such as that illustrated at 1 10, it is necessary under conditions where the motor is lightly loaded that the opening movements of the spool be opposed by a very high-rate spring. Such a spring is illustrated in the assembly of discs 112 which are positioned upon a pin 114 threaded at 116 in the end cap 12 and provided with a lock nut 118 and a closure cap 120. The disc springs 112 are retained on the pin 114 by a stop member 122 having a slot 124 which receives a pin 126 pressed into the pin 114.

The end of the spool 16 abuts a washer 128 which contacts a helical spring 130, the opposite end of which rests within the end of the cap 12. This helical spring and its counterpart at the opposite end cap act as conventional preloaded centering springs. The spool 16 has a recess 132 in its end which receives a piston 134 having an abutment face 136 on its outer end for the purpose of contacting the stop member 122 to compress the disc springs 112. The chamber 132 is connected by a central passage 138 in the spool 16 with that groove or grooves on the spool which are in communication with the high-pressure supply and it thus serves to maintain high pressure within the recess 132 at all times. A check valve 140 prevents displacement of fluid out of the chamber 132 through this path and the only escape from the chamber is that which occurs through leakage past the piston 134, the fit of which within the cylinder 132 is selected for this purpose. A snapring 142 limits the outward movement of the piston 134.

The force-displacement rate of the spring 130 will be much lower than that of the spring assembly 112. Depending upon the distancewhich the spool 16 must travel from its centered position to the point where flow starts to occur, the pin 114 will be adjusted so that stop 122 isjust contacted by the abutment surface 136 at this point. During this travel, only the low rate spring opposes the pressure applied by the pilot control circuit in the opposite end cap. This motion will, of course, have been caused by the operator shifting the handle at the remote control station, first shifting the four-way directional valve so as to exhaust the end cap 12 in which the spring action is occurring and then to apply a progressively increasing pressure to the opposite end cap through progressively increasing the compression of the spring of the relief valve 54. When the abutment 136 and stop 122 come in contact, the disc springs l 12 commence to oppose the pilot pressure in the opposite end cap and from this point on, both the low-rate and the high-rate springs are opposing the pilot pressure. Thus, for a given increment of pilot pressure, only a much smaller movement of the spool 16 occurs. In this way, precise modula tion of the flow at low motor loads may be achieved and, of course, at high motor loads as well. The chamber 132 is maintained at full system pressure by admission of fluid through passage 138 and check valve 140. The area of the piston 134 is so chosen in relation to the system pressure and the maximum force of the fully compressed disc springs 112 that piston 134 is maintained fully projected under these conditions.

Upon further elevation of the pilot control pressure in the opposite end cap, however, the force applied over the full end area of the spool 16 is sufficient to overcome system pressure applied over the area of piston 134 and thus further travel of the spool 16 is permitted to occur. This travel is opposed only by the low-rate spring 130 and by the hydraulic resistance to the exhausting of fluid from chamber 132 past the clearance space around piston 134. Thus, the piston 134 acts as a dash pot to control the further movement of spool 16. The rate of travel of the spool 16 is under the additional control of one or the other of the adjustable restrictors 44. In this way, reliable modulating control of the main directional valve 24 is achieved for both conditions of light and motor loading. Under light loads, almost the full range of flows must be modulated through only a small percentage of the total range of spool travel after opening. Under heavy loads, however, when very little throttling through the directional valve is required, the range of modulation extends throughout the full travel of the spool after opening. The net effect of this type of dual-rate spring mechanism is to give the operator a natural feel at the control handle. When the load is light, modulation of the flow rate or motor speed from zero to full speed is achieved through only about half the range of control lever travel. At heavier loads, a similar modulation of flow rates requires substantially full travel of the control lever to achieve full speed, and in addition there is a softer initial control during which the acceleration of the loaded motor occurs.

The pilot control circuit may be overridden for the purpose of establishing a maximum limit upon flow through the main valve. For this purpose, a bypass valve 144 is mounted on the side of the block 30, its internal construction being illustrated in FIG. 5 and diagrammed within the block 144 in FlG. 4. The valve in FIG. 5 is illustrated in its open position in which the spool 146 connects the two ports 148 and 150 which are connected by lines 152 and 154 with the arms 46 and 48 respec tively of the pilot control circuit. The spool 146 is biased to the left in FIG. 5 by a spring 156 and the ends of the spool are connected so as to be responsive to the pressure drop across an orifice in the main exhaust flow from the valve 24. This orifice is illustrated in FIG. 4 at 158 and may be conveniently located within the exhaust connection flange 20. Suitable conduits such as 160 and 162 serve to sense the pressure in the flange 20 ahead of and beyond the orifice 158 and transmit these pressures through the block 30 to the left and the right ends of the spool 146 in FIG. 5.

In many applications, it is desirable to provide overload protection for the motor which is connected to the flange 22 and for this purpose a relief valve block 164 may be mounted atop the flange 22. This carries internally a single main relief valve 166 connected across the main motor connection A and B. A shuttle valve 168 is arranged to connect the sensing port 170 of relief valve 166 with which ever of the main ports A and B is at the moment under the higher pressure. Conveniently, a drain conduit 172 may lead from the relief valve 166 to join with the conduit 162 for communication with the exhaust line.

The invention thus enables a standard sliding spool directional valve with a slight modification to be used for a modulating control in a central hydraulic system and to permit pilot control from a remote distance through manipulation of a simple pressure relief valve. At the same time, fully effective modulation is achieved, both under conditions requiring a high degree of throttling at the directional valve as well as under conditions which require very little throttling.

I claim:

1. A valve for controlling fluid flow comprising a body having a laterally ported bore, a spool slidable in the bore to control flow between the ports of the bore, pressure actuated pilot means for shifting the spool, a high-rate spring means positioned to oppose the pilot means during a portion of the spool travel, a low-rate spring means positioned so as to oppose the pilot means during at least the remainder of the spool travel, a yieldable abutment contacting one end of the high-rate spring, fluid-operated means for controlling the yieldable abutment, and means for applying and modulating a supply of pressure fluid to the pilot means. 7

2. A valve as defined in claim 1 wherein the means for controlling the abutment comprises a piston slidable in the spool and supporting the yieldable abutment.

3. A valve as defined in claim 2 wherein means is provided for supplying the pressure fluid to the piston to resist yielding of the abutment during compression of the high-rate spring.

4. A valve as defined in claim 2 wherein means is provided for allowing escape of pressure fluid from the piston after the high-rate spring is fully compressed.

5. A valve as defined in claim 1 which includes means for holding the abutment against yielding during the compression of the high-rate spring and allowing yielding after the high-rate spring is fully compressed.

6. A directional control valve comprising a body having a laterally ported bore, a spool slidable in the bore to control flow between the ports of the bore, pressure actuated pilot means for shifting the spool, there being one pilot means at each end of the spool, spring means at each end of the spool to oppose with a predetermined gradient the pilot means at the opposite end of the spool, a pilot fluid pressure circuit comprising a high pressure source, a pair of branches, each containing a fixed restriction and a first arm connected to one of the pilot means and a second arm, a pilot four-way directional valve connected to each of the second arms, a variable pressure relief valve, and an open exhaust path selectively connectable to either of the second arms by shifting the four-way valve, and a single manual lever for shifting the four-way valve in one direction or the other and connected to operate the relief valve during the latter portion of its travel in either direction.

7. A valve as defined in claim 6 wherein each branch includes a variable restrictor and a check valve in parallel in the first arm to limit the maximum rate of travel of the spool.

8. A valve as defined in claim 6 wherein there is provided a bypass valve which when open connects the two branches together, and means responsive to the flow rate controlled by the spool for actuating the bypass valve.

9. A directional control valve comprising a body having a laterally ported bore, a spool slidable in the bore to control flow between the ports of the bore, pressure actuated pilot means for shifting the spool, there being one pilot means at each end of the spool, means for applying and modulating pressure fluid at any desired level to one or the other of the pilot means, and spring means for opposing each pilot means and having a force-displacement rate which is high during initial flow across the spool and decreases thereafter.

10. A valve as defined in claim 9 wherein the spring means includes a series of disc springs for imposing a high force-displacement rate and a helical spring for im osing a lower rate.

11. A valve as defined in claim 10 w erein fluid pressure operated means is provided to allow travel of the spool while the disc springs are fully compressed.

12. A valve as defined in claim 11 wherein the fluid pressure operated means includes a piston in the valve spool and means for applying system pressure to the piston. 

1. A valve for controlling fluid flow comprising a body having a laterally ported bore, a spool slidable in the bore to control flow between the ports of the bore, pressure actuated pilot means for shifting the spool, a high-rate spring means positioned to oppose the pilot means during a portion of the spool travel, a low-rate spring means positioned so as to oppose the pilot means during at least the remainder of the spool travel, a yieldable abutment contacting one end of the high-rate spring, fluidoperated means for controlling the yieldable abutment, and means for applying and modulating a supply of pressure fluid to the pilot means.
 2. A valve as defined in claim 1 wherein the means for controlling the abutment comprises a piston slidable in the spool and supporting the yieldable abutment.
 3. A valve as defined in claim 2 wherein means is provided for supplying the pressure fluid to the piston to resist yielding of the abutment during compression of the high-rate spring.
 4. A valve as defined in claim 2 wherein means is provided for allowing escape of pressure fluid from the piston after the high-rate spring is fully compressed.
 5. A valve as defined in claim 1 which includes means for holding the abutment against yielding during the compression of the high-rate spring and allowing yielding after the high-rate spring is fully compressed.
 6. A directional control valve comprising a body having a laterally ported bore, a spool slidable in the bore to control flow between the ports of the bore, pressure actuated pilot means for shifting the spool, there being one pilot means at each end of the spool, spring means at each end of the spool to oppose with a predetermined gradient the pilot means at the opposite end of the spool, a pilot fluid pressure circuit comprising a high pressure source, a pair of branches, each containing a fixed restriction and a first arm connected to one of the pilot means and a second arm, a pilot four-way directional valve connected to each of the second arms, a variable pressure relief valve, and an open exhaust path selectively connectable to either of the second arms by shifting the four-way valve, and a single manual lever for shifting the four-way valve in one direction or the other and connected to operate the relief valve during the latter portion of its travel in either direction.
 7. A valve as defined in claim 6 wherein each branch includes a variable restrictor and a check valve in parallel in the first arm to limit the maximum rate of travel of the spool.
 8. A valve as defined in claim 6 wherein there is provided a bypass valve which when open connects the two branches together, and means responsive to the flow rate controlled by the spool for actuating the bypass valve.
 9. A directional control valve comprising a body having a laterally ported bore, a spool slidable in the bore to control flow between the ports of the bore, pressure actuated pilot means for shifting the spool, there being one pilot means at each end of the spool, means for applying and modulating pressure fluid at any desired level to one or the other of the pilot means, and spring means for opposing each pilot means and having a force-displacement rate which is high during initial flow across the spool and decreases thereafter.
 10. A valve as defined in claim 9 wherein the spring means includes a series of disc springs for imposing a high force-displacement rate and a helical spring for imposing a lower rate.
 11. A valve as defined in claim 10 wherein fluid pressure operated means is provided to allow travel of the spool while the disc springs are fully compressed.
 12. A valve as defined in claim 11 wherein the fluid pressure operated means includes a piston in the valve spool and means for applying system pressure to the piston. 